1. Field of the Invention
This invention relates to a failure diagnosis apparatus for diagnosing a failure of an evaporative fuel processing system which temporarily stores evaporative fuel generated in a fuel tank and supplies the stored evaporative fuel to an internal combustion engine.
2. Description of the Related Art
A failure diagnosis apparatus for determining whether or not there is a leak in an evaporative fuel processing system after stoppage of an internal combustion engine is disclosed, for example, in Japanese Patent Laid-Open No. 2002-357164. According to this apparatus, air is pressurized by a motor pump and introduced into the evaporative fuel processing system. The determination of whether there is a leak is performed based on a load current value of the motor pump upon air-pressurization. Specifically, if there is a leak in the evaporative fuel processing system, the load current value of the motor pump decreases. Therefore, it is determined that there is a leak when the load current value during air-pressurization is lower than a predetermined determination threshold value.
The conventional apparatus described above requires a motor pump for air-pressurization and raises a problem that the configuration of the apparatus becomes complicated, thereby increasing manufacturing cost. The conventional apparatus further raises a problem that, if there is a leak, evaporative fuel in the evaporative fuel processing system is emitted into the atmosphere by the air-pressurization.